Carburetor



s. F. HUN-r sept 24, 1940.'

GAR-BURETOR Filed Jan. 25, 1934 l l 'nl lllulllIl/A INVENToR.

Sco# E Hum BY .Q $1 @M y Am() EY Patented sept. 24, i940 UNITED STATES CARBURETOR Scott F. Hunt, South Bend, Ind., assignor to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application January 23, 1934, Serial No. 707,942

8 Claims.

This invention relates to carburetors, and more particularly to automaticchoke control mechanism, and is an improvement on the mechanism disclosed in my copending application No. 630,274,

filed August 24, 1932.

In the operation of internal-combustion engines using liquid fuel, it is customary to incorporate some kind of choke valve in the carburetor for the purpose of enriching the mixture to l0 start the engine and for operation while the engine is heating up. Since it is impossible for the operator to determine the most advantageous mixture setting to give greatest eiliciency, and since the mixture ratio must be changed gradually as the engine warms up, it has been found that better results may be obtained by the use of automatic choke control, employing the engine variables, manifold suction and temperature. It is thus possible to provide a mixture that will be consistent with the requirements of the engine at all times, and therefore give greater efficiency. Another featureof this invention has to do with a throttle-cracking and fast-idle mecha- 11118111.v It is a further object of this invention to provide an improved choke valve and fast-idle mechanism which will operate automatically to prevent overchoking of the engine while starting, and provide a suitable mixture for warming up purposes.

A further object is to ,provide mechanism In the drawing, wherein similar reference char-l acters refer to similar parts throughout the several views,

Figure 1 is a vertical section of a device embodying the invention;

Figure 2 is a section on line 2-2 of Figure 1; Figure 3 is a. section on line 3-3 of Figure 2;

and

Figure 4 is a section on line 4-4 of Figure 2.

Referring more particularly to Figure 1, there is shown for purposes of illustrating this inven- I tion a. common type of down-draft carburetor (ci. 12s-119) having an upper body section II) and a lower body section I2 fixed to the intake manifold' I4,v The thermostat control mechanism I6 for actuating the choke valve 'is mounted on the exhaust pipe Il or in any other location where it will be sub- 5 jected to the heat generated by the engine in its operation.

Referring to the carburetor, there is shown a choke valve comprising an unbalanced disc I8 mounted on a shaft 20, which is journaled in the 10 walls of the upper body-section III adjacent the air horn 22. A fuel nozzle 24 is positioned to discharge fuel at the most restricted section of a primary venturi 26, which in turn discharges at the most restricted section of a secondary ven- 15 turi 28. Below venturi 28 a butterfly throttle valve 30 of known construction, adapted to control the flow of mixture into the intake manifold I4, is mounted on a shaft 32, which is journaled in the walls of the lower body section I2. 20

Fixed to choke valve shaft 20 by means of a set s crew 33 is a crank 34 which is connected by a link 36 to a second crank 38 xed to shaft 40 of the thermostat control mechanism I6, so that shaft 40 and choke valve I8 operate together. A 25 spiral bimetallic spring 42 has its inner end fixed to shaft 40, its other end being hooked to engage a suitable pin 44 fixed in housing 46 so that the thermostat may urge choke valve I8 toward closed position when the engine is below normal 30 v operating temperatures. y

A double-armed stop member 4'I fixed to housing 46 is used as an index in assembling the automatic choke device. The device is assembled at a specied temperature by closing choke valve 35 I8, moving crank 38 into contact with the stop 41 nearest the carburetor, tightening set screw 33,'thereby clamping crank 34 to shaft 20. The other stop 41 may be used as an index for adjustmcnt should it be found desirable to assemble the thermostat on the opposite side of the carburetor or in inverted position.

A housing 48 (Figure 2), cast integral with the lower body section I2 above throttle valve 30, accommodates a vacuum actuated piston 50 slidable in a cylinder 62 which communicates with the carbureting passage posterior to the throttle through passages 54 and assists in moving the choke valve I8 from the closed position when the engine starts as described below, by rotating arm 56, the end of which fits in a slot 51 in the upper end of piston 50.

Aim 56 is rotatably mounted on a shaft 58, which is journaled in a plate 60 which closes housing 48. The arm 56 is provided with an ear 55 2 62 which is adapted to engage a pin 64 fixed in shaft 58, so that shaft 58 is rotated in a counterclockwise direction as piston 58 is drawn downwardly in cylinder 52.

Shaft 56 also has rotatably mounted thereon a stop member 66 provided with several stepped surfaces 68 of suitable number and size and adapted to engage an adjusting screw carried by one endof an arm 12 ,fixed to throttle shaft 32. Member 66 is yieldingly urged in the counterclockwise direction by a.' spring 14 which con\` nects it with an ear 16 formed on a lever 18, which is fixed to the shaft 58. One end of lever 18 connects through a link 80 with an arm 82 fixed to choke shaft 20 at the opposite side of the air horn from crank 34. The other end of lever 18 is provided with an ear 84 toengage a shoulder 86 formed on stop member 66 to rotate said member in the clockwise direction as choke valve I8 closes, thereby causing adjusting screw 10,

when the throttleis subsequently closed, to engage one of the higher steps 68. producing a faster idle. The throttle is controlled by manual actuating mechanism 92, of usual construction, and is yieldingly urged toward closed position by the usual throttle return spring, indicated diagrammatically at 93. When the throttle is moved to its fully opened position, an ear 88 on arm 12 engages the under surface ofa projection 98 on lever 18, thus rotating lever 18 in the counterclockwise direction and moving the choke valve to partially opened position against the force of thermostatic spring 42, as shown in Figure 1. It is thus apparent that should the engine become flooded the operator may partially open the choke valve to permit the excess fuel to be drawn out The operation is as follows: Assuming that the engine has been fully warmed up andfis stopped and allowed to cool, thermostatic spring 42 will exert a gradually increasing force tending to rotate shaft 40 in the counterclockwise direction, and urging choke valve I8 in the closing direction by means of the above described mechanism consisting of link 36 and cranks 34 and 38.

As choke valve I8 moves toward closed position, arm 82, fixed to choke shaft 20, moves in the clockwise direction and by means of link 80 rotates lever 18 in the clockwise direction. The throttle is of course in fully closed position during this operation. As llever 18 rotates, it acts through ear 84 to rotate stop member 66 with it until the lowermost of stepped surfaces 68 contacts the lateral surface of adjusting screw 18, whereupon further movement of stop member 66 and lever 18 is arrested.

When theoperator wishes to start the engine he opens the throttle a small amount', thereby drawing adjusting screw 10 out of contact with the stepped surface 68 and permitting thermostat spring 42 to move choke valve I8 to closed position. The operator then turns the ignition switch and starts the engine.

As soon as the engine begins to fire, suction will be transmitted from the intake manifold I4 to cylinder 52 through ports 54 drawing piston 58 and arm 56 downward. As arm 56 rotates on shaft 58, ear 62 engages pin 64 and rotates shaft 68 and member 66 which, through the action of shoulder 86 contacting ear 84, carries with it lever 18. I ievef' 18, through link 80 and arm 82, opens choke valve I8 a small amount against the resiltance offered by thermostat spring 42, thus adl mittingair to prevent overchoking of the engine. In this position, choke valve I8 is free to open somewhat-further under the varying force of suction in the carburetor, and against the force exerted by springs 42 and 14. If the throttle actuating mechanism 92 is at closed position during such further opening movement of the choke valve, however, stop member 66 will be held in fixed position by the friction between screw 10 and the cooperating stepped surface 68. A fast idle is therefore maintained during this period as adjusting screw 18 engages one of the higher steps 88 and prevents the throttle from fully closing.

As the engine begins to warm up, bimetallic spring 42 tends to coil more closely upon itself and exerts a decreasing counterclockwise force on shaft 40, allowing choke valve I8 to open more and more widely under the influence of suction in the carburetor.

If the operator accelerates the engine, screw 10 disengages steps 68 and stop member 66 is rotated in the counterclockwise direction by spring 14 so that when the accelerator pedal is released screw 10 may engage one of the lower steps 68. It is thus apparent that several progressively slower idling speeds are provided as the engine warms up.

When the engine is'thoroughly warmed up, the free end of spring 42 disengages pin 44 and therefore exerts no force tending to close choke valve I8, which will remain in full open position,

and adjusting screw 10 will engage the Jlowest of steps 68 thereby producing a normal or slow idle speed of the engine.

If for any reason the engine should become flooded, the operator will fully open the throttle. As the throttle approaches full open position the ear 88 on arm 12 engages the projection 96 of lever 18 and slides thereon, rotating lever 18 in the counterclockwise direction and opening choke valve I8 )oy means of the above described mechanism comprisingn link 80 and arm 82, so that the pumping action of the engine may be applied to draw the excess raw fuel from the cylinders.

It is expressly understood that the scope of this invention is to be limited by nothing appearing herein except the following claims.

I claim:

1. In a carburetor, a pressure responsive air inlet valve, thermostatic means influencing the movement of thesame, a throttle, a stop member fixed thereto, a vacuum controlled motor, and a positive connection for transmitting force from said motor to said air inlet valve, said connection including a member having a plurality of discrete stop surfaces movable into the path of said stop member to limit the closing movement of the throttle.

2. In a carburetor, a pressure responsive choke valve, temperature responsive means urging the choke valve toward closed position when cold, a throttle, a stop member fixed thereto, a motor controlled by vacuum posterior to the throttle, and a connection for transmitting force from said -motor to the choke valve but incapable of transmitting force from the choke valve to said motor, said connection including a rotary member having several discrete surfaces movable into the path of said stop member to limit in vary-` ing degree the closing movement of the throttle.

3. The invention defined in claim l, wherein the vacuum controlled motor comprises a cylinder fixed to the carburetor and communicating therewith posterior to the throttle.

4. In a carburetor, a carbureting passage, a pressure responsive valve controlling the inlet of said carbureting passage, yielding means iniiuencing the rovement of the pressure respon-I sive valve, a throttle controlling the outlet of said carbureting passage, a stop member carried thereby, a motor controlled by vacuum posterior to the throttle, a connection for transmitting force from said motor to the pressure responsive valve, said connection including an idle-control member having a. plurality of discrete surfaces movable into the path of said stop member to variably limit the closing movement of the throttle, and yielding means connecting said idle-control member to another portion of said connection.

5. -In a carburetor, a carbureting passage, a. choke valve controlling the inlet of said carbureting passage, temperature responsive means urging the choke valve closed when cold, a throttle controlling the outlet of said carbureting passage, a stop member carried thereby, a suctioncontrolled motor, and a connection for transmitting force from said motor to the choke valve, said connection including an idle-control member rotatably mounted adjacent the stop member and cooperating therewith to variably limit the closing movement of the throttle, said idle-control member being yieldingly connected to another portion of said connection.

6. The invention defined in claim 5, including means coacting with said connection when the throttle is, moved to open position to partially open the choke valve.

'1. A carburetor of the character described, comprising a body having a passageway therethrough with air and fuel inlets, a manually operable throttle valve having a shaft and controlling flow through said passageway and being freely movable toward open position, said valve being movable to closed engine idling position at the will of the engine operator to control engine idling operation, an adjustable stop member for variably limiting the extent of closing movement of said valve through a range of engine idling positions, said stop member comprising a rotatable member eccentrically mounted on said body and having a plurality of discrete surfaces, said stop member and said throttle shaft being closely adjacent each other, an arm rigidly secured to and movable with said valve, and a stop member on said arm and engageable with said rotatable member on valve closingmovement to limit throttle valve closing movement.

8. A carburetor of the character described, comprising a body having a passageway therethrough with air and fuel inlets, a manually operable throttle valve controlling ow through said passageway and freely movable toward open position, said valve being movable to closed engine idling position at the will of the engine operator to control engine idling operation, an adjustable stop member for limiting the extent of closing movement of said valve, said stop member comprising a member rotatably mounted on said body and having a peripheral surface noncircular about its center of rotation, means movable with said valve and engageable with said 

